Carbonaceous and bituminous deposits

Abstract

Carbonaceous and bituminous sediments include peats, coals, oil-shales and other deposits, which consist to a large extent of altered organic matter. Many contain recognizable remains of plants, including algae. The distinction drawn between carbonaceous and bituminous products is often obscure in the literature and the terms are often used synonymously. Carbonaceous means like coal or containing carbon and refers to the products of diagenetic and low-temperature metamorphic coalification processes. The changes leading to the formation of coal from plant material are initiated by bacterial and fungal decay at the surface and continue during deep burial and structural deformation. In the case of humic coals there is an early conversion of forest and swampy peat materials into humic substances with a relatively high oxygen content. Wood charcoal is produced under high oxidizing circumstances. Bituminous describes the generally soluble (in organic solvents) organic constituents of sediments, especially oil and fatty hydrocarbons. Bitumens are present in humic coals in relatively minor amounts in the form of waxes, resins and spores, but in some bituminous shales can form a high proportion of the total constituents. Oil-shales, which are frequently highly bituminous, derive most of their bitumens from the degradation of algal and animal matter.